With the ever-increasing popularity and competitiveness of golf, substantial effort and resources are currently being expended to improve golf clubs. Much of the recent improvement activity has involved the combination of the use of new and increasingly more sophisticated materials in concert with advanced club-head engineering. For example, modem “wood-type” golf clubs (notably, “drivers,” “fairway woods,” and “utility or hybrid clubs”), with their sophisticated shafts and non-wooden club-heads, bear little resemblance to the “wood” drivers, low-loft long-irons, and higher numbered fairway woods used years ago. These modem wood-type clubs are generally called “metalwoods” since they tend to be made of strong, lightweight metals, such as titanium.
An exemplary metalwood golf club such as a driver or fairway wood typically includes a hollow shaft having a lower end to which the club-head is attached. Most modern versions of these club-heads are made, at least in part, of a lightweight but strong metal such as titanium alloy. In most cases, the club-head comprises a body to which a face plate (used interchangeably herein with the terms “face” or “face insert” or “striking plate” or “strike plate”) is attached or integrally formed. The strike plate defines a front surface or strike face that actually contacts the golf ball.
Some current approaches to reducing structural mass of a metalwood club-head are directed to making at least a portion of the club-head of an alternative material. Whereas the bodies and face plates of most current metalwoods are made of titanium alloy, several club-heads are available that are made, at least in part, of components formed from either graphite/epoxy-composite (or other suitable composite material) and a metal alloy. Graphite composites have a density of approximately 1.5 g/cm3, compared to titanium alloy which has a density of 4.5 g/cm3, which offers tantalizing prospects for providing more discretionary mass in the club-head.
The ability to utilize such materials to increase the discretionary mass available for placement at various points in the club-head allows for optimization of a number of physical properties of the club-head which can greatly impact the performance obtained by the user. Forgiveness on a golf shot is generally maximized by configuring the golf club head such that the center of gravity (“CG”) of the golf club head is optimally located and the moment of inertia (“MOI”) of the golf club head is maximized.
However, to date there have been relatively few golf club head constructions involving a polymeric material as an integral component of the design. Although such materials possess the requisite light weight to provide for significant weight savings, it is often difficult to utilize these materials in areas of the club head subject to stresses resulting from the high speed impact of the golf ball.
For example, some current metalwoods incorporate weight tracks in the sole to support slidable weights which allow the golfer to adjust the performance characteristics of the club by changing the weight position and effective center of gravity (CG) of the club head. The weight track is generally made from cast titanium to handle the high stress resulting from the high speed impact of the golf ball. Although titanium and titanium alloys are comparatively light in the context of other metals, titanium is still relatively heavy, requires a number of reinforcing ribs and produces undesirably low first modal frequencies (when the ball is struck). A heavier construction for the weight track and ribs means less discretionary weight is available for placement in strategic locations that benefit club performance.
Another recent trend in the industry is to make the club head out of strong, yet lightweight materials such as, for example, titanium, titanium alloys, steel alloys or a carbon fiber composite material. Of these materials, carbon fiber composites are particularly interesting to golf club designers because it has a density that is roughly one third of the density of titanium but is almost as strong as titanium.
Despite the strength and low density of carbon fiber composites, club heads that are made entirely of carbon fiber composites are generally not popular. This is due, in part, to the relatively high stiffness that is typical of carbon fiber composites. Moreover, carbon fiber composites are not particularly durable. Thus, composite club heads have a tendency to wear out in the areas that are subjected to large amounts of wear and friction (e.g., the sole of the club head).
To overcome the above-identified issues, a variety of multi-material metal-composite club heads have been developed. In one example, a metal-composite golf club head has a main metal body with a cast opening located on top of the metal body opposite the sole of the club head. The periphery of the opening includes an inner peripheral flange configured to mate with a peripheral edge of a top cover or “crown plate” or shell made of a composite material (e.g., carbon fiber or graphite). The crown plate is sized and shaped to fit within the top opening such that the peripheral edge of the crown plate mates with the inner peripheral flange of the opening along the entire periphery of the crown plate. In this way, the crown plate completely covers and seals the cast opening. During manufacturing, however, tolerance variations in the dimensions of the main metal body, the cast opening and/or the crown plate can cause the adjoining surfaces at the interface or joint between the crown plate and metal body to be uneven (i.e., not flush). Such fluctuations at these joints cause serious cosmetic defects that must be corrected, resulting in higher manufacturing times and costs and reduced yield of finished products.
When manufacturing conventional multi-material metal-composite club heads, in order to achieve a flush fit between the main body and the crown plate, one or both of the components (e.g., a top plate of the main body and/or the crown plate), is typically made thicker than necessary so that one or both components can be ground down to achieve a flush fit at the joint. Alternatively, or additionally, an extra amount of epoxy or other bonding material can be applied between adjoining surfaces at the joint between the mating components such that a significant amount of epoxy/bonding material will typically accumulate over the joint. This excess epoxy or bonding material, after it is cured, must then be ground down to achieve a flush surface at the joint, and thereafter painted to achieve a desired finished appearance. Needless to say, grinding down one or both components and/or grinding down excess epoxy increases the amount of time and labor necessary to manufacture a finished multi-material metal-composite club head.
In addition to the above problems associated with conventional multi-material metal-composite club heads, the above-described processes of grinding down extra component material and/or grinding down excess bonding material adds an undesired variability in the final weight of the club head, which can adversely affect the performance or “feel” of the club to a user. Furthermore, since any areas that must be ground down must be painted over to achieve a finished appearance, the amount of composite material surface area that remains visible to a user is significantly decreased. Additionally, even after grinding of excess material and/or bonding material is performed, as described above, if there is still a small amount of unevenness at the joint due to the top surface of the crown plate being slightly higher or lower than an adjacent top surface of the main body, the paint covering the joint will show a faint line where the unevenness exists. This faint line is referred to as “ghosting” and is undesirable because it imparts an aesthetic of “cheapness” or “poor design” to a user of the golf club.
In view of the above-described problems associated with conventional multi-material material golf club heads and their methods of manufacture, there is a need for improved golf club head designs and methods of manufacture that address one or more of the above-identified problems.